(1) Field of the Invention
The present invention relates to an integrated motor propulsor comprising a free rotating duct assembly. More specifically, the present invention relates to a free rotating duct assembly incorporating a stator and outboard blades to provide counter-torque rotation about a plurality of rotor blades.
(2) Description of the Prior Art
The Integrated Motor Propulsor (IMP) is a propulsor design concept which integrates an electric motor with the moving parts of a ducted propeller. With reference to FIG. 1, there is illustrated a cross sectional rendering of the basic concept of an IMP 10. The centerline of an underwater vehicle is identified as 12 and the mouth of the ducted propeller is identified as 14. The rotor blades 16 of the propulsor act as the rotors of the motor while the stator 18 is housed in a duct assembly 20 encapsulating and encircling the rotor blades 16 about center line 12. In the IMP design of FIG. 1, permanent magnets 21 are positioned on the outside of rotor blades 16.
This propulsor design is ideal for isolating the propulsor 10 from the main vehicle body 22 and can provide high efficiency. The IMP 10 requires large physical duct supports 24 tying the duct assembly 20 to the vehicle body 22. Electrical current is provided from the vehicle to the stator 18 via an electrical connection 26 extending through support 24. These physical duct supports 24 on the IMP 10 are required to hold the duct assembly 20 stationary while large torques are applied to the rotor blades 16 as they spin about center line 12 under a load.
Although it is possible to engineer suitably large physical duct supports 24 to properly constrain the duct assembly 20, the hydroacoustic impact of having large struts upstream or downstream of the propulsor 10 can be significant. Blade rate tonals are produced when the disturbances from the rotor blades 16 periodically impact the duct supports 24.
What is therefore needed is an IMP design concept that eliminates the duct supports.
Accordingly, it is an object of the present invention to provide a free rotating duct assembly incorporating a stator and outboard blades to provide counter-torque rotation about a plurality of rotor blades.
In accordance with the present invention, an integrated motor propulsor includes a rotor having a plurality of rotor blades adapted to rotate about a center axis. Each of the plurality of rotor blades radially extends in a direction from the center axis to a terminus. A circular outer ring is in contact with the terminus of one of the rotor blades. A duct assembly is circumferentially disposed about the circular outer ring and in low friction contact with the circular outer ring. The duct assembly has a plurality of stators encircling the outer ring, and a plurality of outboard blades extending radially from the duct assembly. Each outboard blade is attached to a pitch control apparatus located in the duct.